BR112013000710B1 - PROCESS FOR THE PRODUCTION OF PARA-XYLENE - Google Patents

Abstract

PROCESS FOR THE PRODUCTION OF PARAXYLENE A reforming process using a medium pore zeolite under conditions to facilitate the conversion of paraffinic C8 compounds to paraxylene is provided. Para-xylene is produced in concentrations greater than thermodynamic equilibrium concentrations using the process.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a process for the production of para-xylene from a paraffinic feed material containing C8. A shape selective catalyst comprising a medium pore zeolite with a silica to alumina ratio of at least 40:1 is used during the catalytic reaction.

BACKGROUND

[0002] Catalytic reforming is one of the basic petroleum refining processes to increase light hydrocarbon feedstocks, often termed as naphtha feedstocks. Catalytic reforming products can include high-octane gasoline useful as automotive fuel, aromatics (eg, benzene, toluene, xylenes, and ethylbenzene), and/or hydrogen. Reactions typically involved in catalytic reforming include dehydrocyclization, isomerization and dehydrogenation of hydrocarbons in the naphtha range, with dehydrocyclization and dehydrogenation of linear and slightly branched alkanes and dehydrogenation of cycloparaffins leading to the production of aromatics. Dealkylation and hydrocracking during catalytic reforming are generally undesirable due to the low value of the resulting light hydrocarbon products.

[0003] Xylene is composed of three different isomers, para-xylene (PX), meta-xylene (MX) and ortho-xylene (OX). Of the xylene isomers, para-xylene (PX) is of particular value, as it is useful for the manufacture of terephthalic acid which is an intermediate in the manufacture of synthetic fibers. A current method to produce para-xylene is to use naphtha reforming, where mixed aromatics are produced. An aromatic-containing stream can be separated and the stream used as a feed material for para-xylene production. Generally, para-xylene is produced together with other isomers of xylene and toluene. Purified toluene can be selectively or non-selectively disproportionated to produce para-xylene and benzene. Para-xylene can also be produced from mixed xylenes by isomerization followed by separation of para-xylene from meta and ortho isomers.

[0004] A known method to produce xylenes involves the alkylation of toluene with methanol over a solid acid catalyst. The alkylation of toluene with methanol on cation-exchanged zeolite Y has been described by, for example, Yashima et al. in Journal of Catalysis 16, 273-280 (1970). Under optimized reaction conditions, the amount of para-xylene produced was approximately 50% by weight of the xylene product mixture.

[0005] US Patent 7,119,239 and US Patent 7,176,339 disclose a process for producing xylenes from reformate. The process is carried out by methylating, under conditions effective for methylation, the benzene/toluene present in the reformate to produce a resultant product having a higher xylene content than the reformate. Larger than equilibrium amounts of para-xylene can be produced by the process. US Patent 7,186,873 discloses a process for producing xylenes from reformate by reactive distillation. The process is carried out by methylating the benzene/toluene present in the reformate in a reactive distillation zone and under reactive distillation conditions to produce a resultant product having a higher xylene content than that of the reformate. Larger than equilibrium amounts of para-xylene can be produced by the process.

[0006] Given the higher demand for para-xylene compared to other xylene isomers, there is significant commercial interest in maximizing para-xylene production from any given source of C8 feed material. However, there are two major technical challenges to achieving this goal of maximizing para-xylene yield. Firstly, the four C8 aromatic compounds, para-xylene, meta-xylene, ortho-xylene and ethylbenzene are generally present in concentrations dictated by thermodynamic equilibria, where meta-xylene comprises about 60% by weight, para-xylene about 14% by weight, orthoxylene about 9% by weight and ethylbenzene about 17% by weight of the C8 aromatics. As a result, para-xylene yield is limited from any refinery C8 stream unless additional processing steps are used to increase the amount of para-xylene and/or to improve para-xylene recovery efficiency. Second, C8 aromatics are difficult to separate because of their similar chemical structures and physical properties and identical molecular weights.

[0007] A variety of methods are known to increase the concentration of para-xylene in a C8 aromatic product stream. These methods typically involve recycling the product stream between a separation step, in which at least part of the para-xylene is recovered to produce a spent para-xylene stream, and a xylene isomerization step, in which the xylene content para-xylene from the depleted stream of para-xylene is returned to equilibrium concentration, typically by contact with a molecular sieve catalyst. However, the commercial utility of these methods depends on the efficiency, cost-effectiveness and speed of the separation step which, as discussed above, are complicated by the chemical and physical similarity of the different C8 isomers.

[0008] A variety of methods are known in the art to purify para-xylene from less valuable xylene isomers and ethylbenzene. Fractional distillation is a commonly used method to separate different components in chemical mixtures. However, it is difficult to use conventional fractional distillation technologies to separate ethylbenzene (EB) and the different xylene isomers, because the boiling points of the four C8 aromatics fall within a very narrow range, i.e. around 136°C. at about 144°C. In particular, the boiling points of para-xylene and EB are about 2°C apart, whereas the boiling points of para-xylene and meta-xylene are only about 1°C apart. As a result, large equipment, significant energy consumption, and/or substantial recycles would be required for fractional distillation to provide effective C8 aromatic separation. Another method for separating para-xylene from other isomers of xylene and ethylbenzene involves crystallizing para-xylene. US 5,811,629 discloses a process for purifying para-xylene from C8 aromatics involving at least two crystallization stages, as well as at least one recycle step and at least one additional separation step. The methods described above are time consuming and expensive. It is desirable to increase the amount of para-xylene in the product stream in order to minimize the number of recycle and purification steps required to obtain pure para-xylene product.

[0009] The use of a low acidity medium pore zeolite catalyst with a silica to alumina ratio of at least about 40 to 1 has been found to increase the yield of para-xylene from a given xylene material. paraffin feed C8.

SUMMARY OF THE INVENTION

[0010] The present invention provides a process for producing para-xylene comprising the steps of: supplying a C8-containing feed material which contains at least 10% by weight of paraffinic C8 hydrocarbons to a reforming reaction zone containing a catalyst of reforming comprising a medium pore zeolite having a silica to alumina molar ratio of at least 200 and a crystallite size of less than 10 microns; contacting the C8-containing feed material under reforming reaction conditions in the reforming reaction zone to produce para-xylene and meta-xylene at a weight ratio of para-xylene to meta-xylene of at least 0.9; and separating the para-xylene from the meta-xylene.

[0011] In another embodiment, the present invention provides a process for producing para-xylene comprising the steps of: contacting a hydrocarbonaceous feed in which at least 50% by weight of said feed boils above 560.93 K (550°F) in a first reaction zone comprising a hydrocracking catalyst under hydrocracking conditions to form an effluent; separating the effluent into at least one C8-containing fraction comprising at least 10% by weight of C8 paraffinic hydrocarbons; feeding the C8-containing fraction to a second reaction zone; contacting the C8-containing fraction under reforming reaction conditions with a reforming catalyst comprising a medium pore zeolite having a silica to alumina mole ratio of at least 200, a crystallite size of less than 10 microns and an alkaline content of less than 5,000 ppm into a second reaction zone to produce a product stream comprising para-xylene and meta-xylene, wherein the ratio of para-xylene to meta-xylene is at least 0.9; and separating the para-xylene from the product stream.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Fig. 1 is a schematic diagram of an embodiment of the invention.

DETAILED DESCRIPTION

[0013] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are described in detail herein. It should be understood, however, that the present description of specific embodiments is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as such. as defined by the appended claims.

[0014] The present invention relates to a process for increasing or maximizing the production and/or yield of para-xylene (PX) in chemical plants and refineries, where feed materials comprising C8 paraffinic compounds are separated, produced and/or processed. The present invention also relates to a para-xylene-containing product produced by such a process or in such a factory. In one embodiment, the process of the invention utilizes a naphtha-boiling feed material comprising at least about 10% by weight of C8 paraffinic hydrocarbons. In one embodiment, the feed material can boil in the range of about 283.15 K (50°F) to about 560.93 K (550°F) and more typically in the range of about 294.26 K (70°F). °F) to about 505.37 K (450°F).

[0015] The present invention provides a process for making para-xylene from a paraffinic feed material containing C8. In one embodiment, by "C8-containing paraffinic feedstock" is meant a feedstock generally containing at least about 5% by weight of C8 paraffinic hydrocarbons, more typically at least about 10% by weight of C8 paraffinic hydrocarbons. C8 paraffinic hydrocarbons, and often at least about 12% by weight of C8 paraffinic hydrocarbons, and even at least about 15% by weight of C8 paraffinic hydrocarbons. In a separate embodiment, by "C8-containing paraffinic feed material" is meant a feed material generally containing at least about 40% by weight of C8 paraffinic hydrocarbons, and more typically at least about 50% by weight. C8 paraffinic hydrocarbons by weight and often at least about 60% by weight C8 paraffinic hydrocarbons. Paraffinic C8-containing feedstock also generally contains less than 20% by weight of C10+ hydrocarbons, more typically less than 10% by weight of C10+ hydrocarbons and often less than 5% by weight of C10+ hydrocarbons, and even less than 1% by weight of C10+ hydrocarbons. In general, the presence of aromatics in the feed, including the C8 para-xylene, meta-xylene, ortho-xylene and/or ethylbenzene isomers is not detrimental to the process. For example, the feed material can contain up to 1% by weight of para-xylene, up to 2% by weight of para-xylene, or even greater amounts of para-xylene. In embodiments, the feed material contains in the range of 0 to 2% by weight of para-xylene.

[0016] In general, the C8-containing feed material may be direct cycle naphtha or its fractions or hydrocracker naphtha, for example, a C8 cut downstream of the fractionating column of a hydrocracker unit. In another embodiment, an effluent from one or more naphtha reforming stages of a multistage reformer is separated by fractional distillation to give at least one fraction containing at least 10% by weight of C8 paraffinic hydrocarbons. The C8 paraffinic feedstock has a boiling range from about 283.15 K (50°F) to about 560.93 K (550°F) and often from about 294.26 K (70°F ) at about 505.37 K (450°F). The paraffinic C8-containing feed material may comprise, for example, direct cycle naphthas, paraffinic raffinates from aromatic extraction or adsorption and C6-C10 paraffin-containing feed, bioderived naphtha, naphtha from hydrocarbon synthesis processes, including hydrocarbon synthesis processes. Fischer-Tropsch and methanol, as well as naphtha products from other refinery processes such as hydrocracking or even conventional reforming.

[0017] In the process of the invention, paraffinic feed material containing C8 is contacted with a catalyst containing a medium pore zeolite under reforming reaction conditions. The catalyst is such that the molar ratio of para-xylene to meta-xylene in the product is greater than the thermodynamic equilibrium ratio PX/MX. Compared to a thermodynamic equilibrium xylene blend in which the ratio of para-xylene to meta-xylene is approximately 0.5:1, the process described herein provides a product having a ratio of para-xylene to meta-xylene greater than 0.9:1. In illustrative embodiments, the product has a molar ratio of para-xylene to meta-xylene greater than 1:1, or greater than 1.1:1 or even greater than 1.2:1. The improved para-xylene yield reduces the cost of production and also minimizes the cost of separating para-xylene from other xylene isomers and ethylbenzene, which is the most expensive step in many methods currently employed to produce para-xylene.

Definitions

[0018] The following terms will be used throughout the descriptive report and will have the following meanings, unless otherwise indicated.

[0019] As used herein, the terms "hydrocarbon" or "hydrocarbonaceous" or "petroleum" are used interchangeably to refer to carbonaceous material originating from crude oil, natural gas or biological processes.

[0020] As used herein, “Group VIB” or “Group VIB metal” refers to one or more metals, or compounds thereof, selected from Group VIB of the Chemical Abstract Services Periodic Table. The Chemical Abstract Services Periodic Table can be found, for example, behind the cover of the CRC Handbook of Chemistry and Physics, 81st Edition, 2000-2001.

[0021] As used herein "Group VIII" or "Group VIII metal" refers to one or more metals or their compounds selected from Group VIII of the Chemical Abstract Services Periodic Table.

[0022] Hydrocracking is a chemical reaction of liquid feed materials, including hydrocarbons, petroleum and other biologically derived material, in the presence of hydrogen and one or more catalysts, resulting in product molecules having reduced molecular weight relative to that of the feed materials liquids. Additional reactions including olefin and aromatic saturation and heteroatom removal (including oxygen, nitrogen, sulfur and halogen) can also occur during hydrocracking.

[0023] Reforming is a chemical reaction of liquid feedstocks, including hydrocarbons, petroleum, and other biologically derived material, in the presence of one or more catalysts resulting in product molecules, such as automobile fuel, aromatics (e.g., benzene, toluene, xylenes and ethylbenzene) and/or hydrogen. Reactions typically involved in catalytic reforming include dehydrocyclization, isomerization and dehydrogenation of hydrocarbons in the naphtha range, with dehydrocyclization and dehydrogenation of linear and slightly branched alkanes and dehydrogenation of cycloparaffins leading to the production of aromatics.

[0024] As used herein, a paraffin refers to a non-cyclic, linear or branched, saturated hydrocarbon. For example, a C8 paraffin is a non-cyclic, linear or branched hydrocarbon having 8 carbon atoms per molecule. Normal octane, methylheptanes, dimethylhexanes, trimethylpentanes are examples of C8 paraffins. A paraffin-containing feed comprises non-cyclic saturated hydrocarbons such as normal paraffins, isoparaffins and mixtures thereof.

[0025] As used herein, a naphthene is a type of alkane having one or more rings of carbon atoms in its chemical structure. In embodiments, naphthene is a non-aromatic, cyclic hydrocarbon. In some embodiments, the naphthene is saturated. In some of these embodiments, naphthene is a saturated, cyclic, non-aromatic hydrocarbon having in the range of 5 to 8 carbon atoms in the cyclic structure.

[0026] As used herein, naphtha is a hydrocarbonaceous fraction distilled at boiling point within the range of 283.15 to 560.93 K (50° to 550°F). In some embodiments, naphtha boils within the range of 294.26 to 505.37 K (70° to 450°F), and more typically in the range of 299.8 to 477.59 K (80° to 400° F), and often within the range of 305.37 to 455.37 K (90° to 360°F). In some embodiments, at least 85% by volume of naphtha boils within the range of 50° to 550°F, and more typically within the range of 294.26 to 505.37 K (70° to 450°F) . In embodiments, at least 85% by volume of the naphtha is in the C4-C12 range, and more typically in the C5-C11 range, and often in the C6-C10 range. Naphtha may include, for example, direct cycle naphthas, paraffinic raffinates from aromatic extraction or adsorption, feedstocks containing C6-C10 paraffin, bioderived naphtha, naphtha from hydrocarbon synthesis processes, including Fischer-Tropsch and methanol synthesis processes, as well as naphthas from other refinery processes, such as hydrocracking or conventional reforming.

[0027] As disclosed herein, boiling point temperatures are based on the ASTM D-2887 Standard Test Method for Boiling Range Distribution of Petroleum Fractions by Gas Chromatography, unless otherwise noted. Mean boiling point is defined as the boiling point of 50% by volume, based on an ASTM D-2887 simulated distillation.

[0028] As disclosed herein, carbon number values (i.e., C5, C6, C8, C9 and the like) of hydrocarbons can be determined by standard gas chromatography methods.

[0029] Unless otherwise specified, the feed rate for a catalytic reaction zone is reported as the feed volume per hour per volume of catalyst. Indeed, the feeding rate as disclosed herein, called net hourly space velocity (LHSV), is reported in reciprocal hours (i.e., h-1).

[0030] The term “silica to alumina ratio” refers to the molar ratio of silicon oxide (SiO2) to aluminum oxide (A12O3). ICP analysis can be used to determine the silica to alumina ratio.

[0031] As used herein, the value for octane refers to the research octane number (RON) as determined by ASTM D2699-09.

[0032] As used herein, the amount of pressure in units of psig (pounds per square inch) is reported as “gauge” pressure, that is, absolute pressure minus ambient pressure, unless otherwise noted. The amount of pressure in units of either psi (pounds per square inch) or kPa (kilopascal) is reported as absolute pressure unless otherwise noted.

[0033] As used herein “penultimate stage” does not necessarily refer to the second to last stage in a multistage reform process, but rather refers to a stage preceding at least one additional stage. As used herein, “final stage” does not necessarily refer to the last stage of a multi-stage reform process, but rather refers to the stage after a penultimate stage.

[0034] The equilibrium reaction for the conversion of toluene to xylene and benzene products typically yields about 24% by weight of para-xylene (PX), about 54% by weight of meta-xylene (MX) and about 22 % by weight of ortho-xylene (OX) among xylenes. For a more complete description of equilibrium product distributions for xylene isomerization see R.D. Chirico and W.V. Steele, “Thermodynamic Equilibria in xylene isomerization. 5. Xylene isomerization equilibria from thermodynamic studies and reconciliation of calculated and experimental product distributions”, Journal of Chemical Engineering Data, 1997, 42(4), 784-790, incorporated herein by reference in its entirety.

[0035] The catalysts employed in the process of the invention can be employed in the form of pills, pellets, granules, broken fragments or various special forms, arranged as a fixed bed within a reaction zone, and the feed material can be passed through even in liquid, vapor or mixed phase, and in ascending, descending or radial flow. Alternatively, they can be used in moving beds or fluidized solid processes, in which the feedstock is passed upward through a turbulent bed of finely divided catalyst. However, a fixed bed system or a dense phase moving bed system are preferred due to lower catalyst attrition losses and other operational advantages. In a fixed bed system, the feed may be preheated (by any suitable heating means) to the desired reaction temperature and then passed into a reaction zone containing a fixed bed of catalyst. This reaction zone can be one or more separate reactors. hydrocracking

[0036] The hydrocracking reaction zone is maintained in conditions sufficient to effect a boiling range conversion of the hydrocarbon feedstock to the hydrocracking reaction zone, so that the liquid hydrocracked recovered from the hydrocracking reaction zone has a normal boiling point range below the feed boiling point range. The hydrocracking step reduces the size of hydrocarbon molecules, olefin bonds of hydrogenates, aromatics of hydrogenates and removes trace heteroatoms resulting in an improved product quality of base oil or fuel.

[0037] The hydrocracking catalyst generally comprises a cracking component, a hydrogenation component and a binder. Such catalysts are well known in the art. The cracking component may include an amorphous silica/alumina phase and/or a zeolite, such as a Y-type or USY-type zeolite. If present, the zeolite is at least about 1 percent by weight based on the total weight of the catalyst. A zeolite-containing hydrocracking catalyst generally contains in the range of 1% by weight to 99% by weight of zeolite, and more typically in the range of 2% by weight to 70% by weight of zeolite. Actual amounts of zeolite will, of course, be adjusted to meet catalytic performance requirements. The binder is usually silica or alumina. The hydrogenation component will be a Group VI, Group VII, or Group VIII metal or oxides or sulfides thereof, preferably one or more of molybdenum, tungsten, cobalt or nickel, or the sulfides or oxides thereof. If present in the catalyst, these hydrogenation components generally make up from about 5% to about 40% by weight of the catalyst. Alternatively, platinum group metals, especially platinum and/or palladium, may be present as the hydrogenation component, either alone or in combination with the molybdenum, tungsten, cobalt or nickel base metal hydrogenation components. If present, the platinum group metals will generally comprise from about 0.1% to about 2% by weight of the catalyst.

[0038] The process of the invention can employ a wide variety of hydrocarbon feedstocks from many different sources, such as crude oil, virgin petroleum fractions, petroleum recycle fractions, shale oil, liquefied coal, petroleum tar sand, normal alpha olefin synthetic paraffins, recycled plastic feedstocks, petroleum distillates, solvent-asphalted petroleum waste, shale oils, coal tar distillates, hydrocarbon feedstocks derived from plant, animal sources and/or algae and combinations thereof. Other feed materials that can be used in the process of the invention include synthetic feeds, such as those derived from a Fischer Tropsch process. Other suitable feed materials include those heavy distillates commonly defined as heavy straight cycle gas oils and heavy cracked cycle oils, as well as conventional fluid catalytic crack feeds and portions thereof. In general, the feed can be any carbon-containing feed material susceptible to catalytic hydroprocessing reactions, particularly hydrocracking and/or reforming reactions. A suitable liquid hydrocracker feed material is a vacuum gas oil boiling over a temperature range above about 450°F (505.37 K) (232°C) and more typically within the temperature range of 560.93 to 866.48 K (550° to 1100°F) (288 to 593°C). In embodiments, at least 50% by weight of the hydrocarbon feed material boils above 560.93 K (550°F) (288°C). The term liquid refers to hydrocarbons that are liquid under ambient conditions.

[0039] The liquid hydrocracker feed material that may be used in the present invention contains impurities such as nitrogen and sulfur, at least some of which are removed from the hydrocarbon feed material in the hydrocracking zone. Nitrogen impurities present in the hydrocarbonaceous feedstock may be present as organonitrogen compounds in amounts greater than 1 ppm. Sulfur impurities may also be present. Feeds with high levels of nitrogen and sulfur, including those containing up to 0.5% by weight (and more) nitrogen and up to 2% by weight and above sulfur, can be treated in the present process. However, feedstocks that are rich in asphaltenes and metals will generally require some form of pretreatment, such as in a hydrotreating operation, before they are suitable for use as a feedstock for the hydrocracking process step. A suitable liquid hydrocarbon feedstock generally contains less than about 500 ppm asphaltenes, more typically less than about 200 ppm asphaltenes, and often less than about 100 ppm asphaltenes.

[0040] According to one embodiment, the hydrocarbonaceous feedstock is brought into contact with the hydrocracking catalyst in the presence of hydrogen, generally in a fixed-bed reactor in the hydrocracking reaction zone. Conditions in the hydrocracking reaction zone may vary according to the nature of the feed, the intended quality of the products and the particular facilities at each refinery. Hydrocracking reaction conditions include, for example, a reaction temperature within the range of 505.37 K to 755.37 K (450°F to 900°F) (232°C to 482°C) and typically a reaction temperature in the range of 650°F to 850°F (616.48 to 727.59 K) (343°C to 454°C); a reaction pressure within the range of 500 to 5000 psig (3.5 to 34.5 MPa) and typically a reaction pressure in the range of 1500 to 3500 psig (10.4 to 24.2 MPa); a liquid reagent feed rate, in terms of liquid hourly space velocity (LHSV), within the range of 0.1 to 15 h-1 (v/v), typically in the range of 0.25 to 2.5 h -1; and hydrogen feed rate, in terms of H2/hydrocarbon ratio, within the range of 500 to 5,000 standard cubic feet per barrel of liquid hydrocarbon feed (89.1 to 445 m3 H2/m3 feed). The hydrocracked is then separated into various boiling range fractions. Separation is typically accomplished by fractional distillation preceded by one or more vapor-liquid separators to remove hydrogen and/or other waste gases.

[0041] In some situations, hydrocracking reaction conditions are established to achieve a targeted conversion of the hydrocarbonaceous feed material within the hydrocracking reaction zone. For example, hydrocracking reaction conditions can be adjusted to achieve greater than 30% conversion. As an example, the target conversion can be greater than 40% or 50% or even 60%. As used herein, the conversion is based on a reference temperature such as, for example, the minimum boiling point temperature of the hydrocracker feed. The extent of conversion refers to the percentage of feed boiling above the reference temperature that is converted to products boiling below the reference temperature.

[0042] The hydrocracking reaction zone containing the hydrocracking catalyst may be contained within a single reactor vessel, or it may be contained within two or more reactor vessels connected together in fluid communication in a series arrangement . In embodiments, hydrogen and hydrocarbonaceous feed are supplied to the hydrocracking reaction zone in combination. Additional hydrogen can be supplied at various positions along the length of the reaction zone to maintain an adequate supply of hydrogen to the zone. In addition, the relatively fresh hydrogen added along the length of the reactor can serve to absorb some of the heat energy within the zone and help maintain a relatively constant temperature profile during the exothermic reactions that occur in the reaction zone.

[0043] The catalysts within the hydrocracking reaction zone may be of only one type. In embodiments, multiple types of catalysts can be mixed in the reaction zone, or they can be placed in separate catalyst layers to provide a specific catalytic function that provides improved operation or improved product properties. The catalyst may be present in the reaction zone in a fixed bed configuration, with the hydrocarbonaceous feed passing either up or down through the zone. In embodiments, the hydrocarbonaceous feed passes cocurrently with the hydrogen feed into the zone. In other embodiments, the hydrocarbonaceous feed passes in countercurrent to the hydrogen feed within the zone.

[0044] Hydrocracking reaction zone effluent is the total material passing from the hydrocracking reaction zone and generally includes normally liquid hydrocarbonaceous materials, typically gas phase hydrocarbonaceous reaction products, one or more of H2S, NH3 and H2O from the reaction of heteroatoms with hydrogen in the reaction zone and unreacted hydrogen.

[0045] In general, effluent from the hydrocracking reaction zone is first processed to recover at least a portion of the unreacted hydrogen in one or more initial separation steps, using flash separation or fractional distillation processes. These initial separation steps are well known, and their design and operation are dictated by specific process requirements. Flash separation steps are generally operated at a pressure within the range of ambient pressure to the pressure of the hydrocracking reaction zone and at a temperature within the range of 310.9 K (100°F) to the temperature of the reaction zone. of hydrocracking.

[0046] At least a portion of the effluent from the hydrocracking reaction zone is separated by means of fractional distillation into various fractions based on the initial and final boiling points of the components. In embodiments, the separation is performed in an atmospheric distillation column operated at a pressure approximately equal to or slightly greater than ambient pressures, including a pressure of 0 MPa to 0.689 MPa (0 psig to 100 psig). Distillation fractions from an atmospheric column may include one or more C4 fractions, C5-C8 fraction and one or more C9+ fractions, with each fraction being distinguished by a unique boiling point range. Such atmospheric distillation processes are well known. In embodiments, the residue fraction from atmospheric distillation is further separated in a vacuum distillation column operated at subatmospheric pressure. Distilled fractions from vacuum distillation include one or more fractions of gasoil under vacuum boiling within a range of approximately 500° to 1100°F (533.15 to 866.48 K). In general, a fraction of distillate recovered from distillation is in the vapor phase under distillation conditions but in the liquid phase under ambient conditions; a gaseous overhead fraction recovered from distillation is in the vapor phase under distillation conditions and also in the vapor phase under ambient conditions; and a residual fraction recovered from distillation remains in the liquid phase under distillation conditions.

[0047] In embodiments, the C8-containing paraffin feed material is a hydrocracked naphtha. An exemplary hydrocracked naphtha that is useful in the process is recovered from atmospheric distillation of at least a portion of the effluent from the hydrocracking reaction zone. Examples of hydrocracked naphthas that are recovered from atmospheric distillation generally have a normal boiling point range within the range of 283.15 to 560.93 K (50° to 550°F) and more typically within the range of 294, 26 at 505.37K (70° to 450°F). Distillation can generally be operated to produce a naphtha stream comprising at least 60% by weight of C4 to C10 hydrocarbons, more typically at least 70% by weight of C4 to C10 hydrocarbons and often at least 80% by weight of C4 to C10 hydrocarbons. C10. In embodiments, distillation may generally be operated to produce a naphtha stream comprising at least 60% by weight of C5 to C9 hydrocarbons, more typically at least 70% by weight of C5 to C9 hydrocarbons, and often at least 80 % by weight of C5 to C9 hydrocarbons. In embodiments, the distillation can generally be operated to produce a naphtha stream comprising at least 60% by weight of C6 to C8 hydrocarbons, more typically at least 70% by weight of C6 to C8 hydrocarbons, and often at least 80% by weight. weight of C6 to C8 hydrocarbons.

[0048] In one embodiment, the hydrocracked naphtha generally contains at least about 5% by weight of C8 paraffinic hydrocarbons, more typically at least about 10% by weight of C8 paraffinic hydrocarbons, and often at least about 12% by weight. C8 paraffinic hydrocarbons by weight or at least about 15% by weight of C8 paraffinic hydrocarbons. In a separate embodiment, the hydrocracked naphtha generally contains at least about 40% by weight of C8 paraffinic hydrocarbons, more typically at least about 50% by weight of C8 paraffinic hydrocarbons and often at least about 60% by weight of C8 paraffinic hydrocarbons. paraffinic C8. Adaptation of hydrocracked naphtha to yield a desired C8 paraffinic hydrocarbon content is achieved, at least in part, by selection of distillation design and operating parameters.

[0049] In embodiments, the hydrocracked naphtha contains less than 10% by weight aromatics, more typically less than 5% by weight aromatics and often less than 2% by weight aromatics. In embodiments, the hydrocracked naphtha contains less than 1000 ppm sulfur, more typically less than 100 ppm sulfur and often less than 10 ppm sulfur and even less than 1 ppm sulfur. In embodiments, hydrocracked naphtha contains less than 1000 ppm nitrogen, more typically less than 100 ppm nitrogen and often less than 10 ppm nitrogen and even less than 1 ppm nitrogen. In embodiments, hydrocracked naphtha has an octane number of less than 90, more typically less than 85, often less than 80 and even less than 75.

Remodeling

[0050] The reforming catalyst is selected to provide a high selectivity for the production of aromatic compounds at a reduced pressure, which increases the selectivity of dehydrocyclization of paraffin C6 to C8, while maintaining low rates of catalyst fouling. In embodiments, the reforming catalyst comprises at least one medium pore zeolite. The molecular sieve is a porous inorganic oxide, characterized by a crystalline structure that provides pores of a specified geometry, depending on the particular structure of each molecular sieve. The phrase "average pore", as used herein, means having a crystallographic free diameter in the range of about 3.9 to about 7.1 Angstroms when the porous inorganic oxide is in calcined form. Free crystallographic diameters of molecular sieve channels are published in “Atlas of Zeolite Framework Types”, Fifth Revised Edition, 2001, by Ch. Baerlocher, W.M. Meier and D.H. Olson, Elsevier, pp 10-15, which is incorporated herein by reference. Non-limiting examples of medium pore zeolites include ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48 MCM-22, SSZ-20, SSZ-25, SSZ -32, S8Z-35, SSZ-37, SSZ-44, SSZ-45, SSZ-47, SSZ-58, SSZ-74, SUZ-4, EU-1, NU-85, NU-87, NU-88 , IM-5, TNU-9, ESR-10, TNU-10 and their combinations. In embodiments, the medium pore zeolite is a zeolite which is a crystalline material having three-dimensional structures composed of tetrahedral units (TO4/2, T=Si, Al, or other tetrahedrally coordinated atom) linked through oxygen atoms. A medium pore zeolite that is useful in the present process includes ZSM-5. Several references disclosing ZSM-5 are provided in US Patent 4,401,555 to Miller. Additional disclosure on the preparation and properties of high silica ZSM-5 can be found, for example, in US Patent 5,407,558 and US Patent 5,376,259.

[0051] In embodiments, the reforming catalyst includes a silicate having a form of ZSM-5 with a SIO 2 /M 2 O 3 molar ratio of at least 40:1; or at least 200:1 or at least 500:1, or even at least 1000:1; where M is selected from Al, B or Ga. In embodiments, the ZSM-5 has a silica to alumina mole ratio of at least 40:1, or at least 200:1, or at least 500:1, or even at least 1000:1. The silicate that is useful is further characterized as having a crystallite size of less than 10 µm, or less than 5 µm or even less than 1 µm. Methods for determining crystallite size using, for example, Scanning Electron Microscopy, are well known. The silicate that is useful is also characterized as having at least 80% crystallinity, or at least 90% crystallinity, or at least 95% crystallinity. Methods for determining crystallinity using, for example, X-ray diffraction are well known.

[0052] Strong acidity is undesirable in the catalyst because it promotes cracking resulting in lower selectivity for liquid C5+ product. To reduce acidity, a silicate containing alkali metal and/or alkaline earth metal cations is useful for reforming the naphtha. Alkali or alkaline earth metal cations can be incorporated into the catalyst during or after molecular sieve synthesis. Suitable molecular sieves are characterized by having at least 90% of the acidic sites or at least 95% of the acidic sites, or at least 99% of the acidic sites being neutralized by the introduction of alkaline or alkaline earth cations. In one embodiment, the medium pore zeolite contains less than 5,000 ppm alkaline. Such molecular sieves are disclosed, for example, in US Patent 4,061,724, US Patent 5,182,012 and US Patent 5,169,813. These patents are incorporated herein by reference, in particular with regard to the description, preparation and analysis of molecular sieves having specified silica to alumina mole ratios, having a specified crystallite size, having a specified crystallinity, and having an alkaline content and /or specified alkaline earth.

[0053] In embodiments, the silicate is a ZSM-5 type medium pore zeolite. In some of these embodiments, the silicate is silicalite, a very high silica to alumina ratio form of ZSM-5. In embodiments, the silicalite has a silica to alumina mole ratio of at least 40:1, or at least 200:1, or at least 500:1, or even at least 1000:1. Several references disclosing silicalite and ZSM-5 are provided in US Patent 4,401,555 to Miller and US Patent 6,063,723 to Miller. These references include the aforementioned US Patent 4,061,724 to Grose et al.,. Reissued US Patent 29,948 to Dwyer et al.,. Flanigen et al., Nature, 271, 512516 (February 9, 1978), which discuss the physical and adsorption characteristics of silicalite; and Anderson et al., J. Catalysis 58, 114-130 (1979) which discloses catalytic reactions and sorption measurements performed on ZSM-5 and silicalite. The disclosures of these publications are incorporated herein by reference.

[0054] Other zeolites that can be used in the process of the present invention include those listed in US Patent 4,835,336, namely: ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38 , ZSM-48 and other similar materials.

[0055] ZSM-5 is more particularly described in US Patent 3,702,886 and US Patent Re 29,948, the entire contents of which are incorporated herein by reference.

[0056] ZSM-11 is more particularly described in US Patent 3,709,979 the entire contents of which are incorporated herein by reference.

[0057] ZSM-12 is more particularly described in US Patent 3,832,449, the entire contents of which are incorporated herein by reference.

[0058] ZSM-22 is more particularly described in US Patents 4,481,177; 4,556,477 and EP Patent 102,716, the entire contents of each of which are expressly incorporated herein by reference.

[0059] ZSM-23 is more particularly described in US Patent 4,076,842, the entire contents of which are incorporated herein by reference.

[0060] ZSM-35 is more particularly described in US Patent 4,016,245, the entire contents of which are incorporated herein by reference,

[0061] ZSM-38 is more particularly described in US Patent 4,046,859, the entire contents of which are incorporated herein by reference.

[0062] ZSM-48 is more particularly described in US Patent 4,397,827 the entire contents of which are incorporated herein by reference.

[0063] In embodiments, the crystalline silicate may be in the form of a borosilicate, where the boron replaces at least a portion of the aluminum in the more typical form of aluminosilicate. Borosilicates are described in US Patents 4,268,420; 4,269,813 and 4,327,236 to Klotz, the disclosures of those patents are incorporated herein, particularly that disclosure which relates to the preparation of borosilicate. In a suitable borosilicate, the crystal structure is that of ZSM-5 in terms of standard X-ray diffraction. Boron in ZSM-5 type borosilicates replaces the aluminum that is present in the more typical ZSM-5 crystalline aluminosilicate structures. Borosilicates contain boron rather than aluminum, but there are usually some trace amounts of aluminum present in crystalline borosilicates.

[0064] Still more crystalline silicates that can be used in the present invention are ferrosilicates, as disclosed, for example, in US Patent 4,238,318, gallosilicates, as disclosed, for example, in US Patent 4,636,483, and chromosilicates as disclosed, for example, in US Patent 4,299,808.

[0065] The reforming catalyst further contains one or more Group VIII metals, for example, nickel, ruthenium, rhodium, palladium, iridium, or platinum. In embodiments, Group VIII metals include iridium, palladium, platinum or a combination thereof. These metals are more selective with regard to dehydrocyclization and are also more stable under dehydrocyclization reaction conditions than other Group VIII metals. When employed in the reforming catalyst, these metals are generally present in the range between 0.1% by weight and 5% by weight or between 0.3% by weight and 2.5% by weight. The catalyst may also comprise a promoter, such as rhenium, tin, germanium, cobalt, nickel, iridium, tungsten, rhodium, ruthenium, or combinations thereof. In an illustrative embodiment, the catalyst comprises in the range of 0.1% by weight to 1% by weight of platinum and in the range of 0.1% by weight to 1% by weight of rhenium.

[0066] In forming the reforming catalyst, the crystalline molecular sieve is preferably bound to a matrix. Suitable matrices include inorganic oxides, including alumina, silica, naturally occurring and conventionally processed clays, such as bentonite, kaolin, sepiolite, attapulgite and halloysite.

[0067] The actual reaction conditions employed in the process of the invention will depend, at least in part, on the feed used, whether highly aromatic, paraffinic or naphthenic. The reaction conditions of temperature, pressure, hydrocarbon to hydrogen ratio and LHSV can be tuned to maximize para-xylene production.

[0068] The process for producing para-xylene includes reforming naphtha over a silicate catalyst. In one embodiment, the process of the invention for producing para-xylene can be incorporated into a multistage naphtha reforming process. The naphtha reforming conditions can be chosen such that the feedstock used in the process of the invention comprises at least about 10% C8 paraffinic hydrocarbons. For example, effluent from a penultimate stage of a multistage naphtha reforming process, wherein the effluent contains at least about 5% by weight of C8 paraffinic hydrocarbons, or at least about 10% by weight of paraffinic hydrocarbons C8, or at least about 12% by weight of C8 paraffinic hydrocarbons, or even at least about 15% by weight of C8 paraffinic hydrocarbons can be contacted with the catalyst used in the process of the present invention in a separate stage under reaction conditions of para-xylene formation, including a temperature in the range of about 699.8 K (800°F) to about 866.48 K (1100°F), a pressure in the range of about 1 to about 6, 89 MPa (1000 psig), or from about 0 MPa (0 psig) to about 2.41 MPa (350 psig) and a feed rate in the range of about 0.1 h-1 to about 20 h- 1 of LHSV. Hydrogen can be added as an additional feed to the stage in which para-xylene is produced, if needed. Hydrogen can be generated by the process of the invention, depending on the feedstock. This hydrogen can be recycled back to the reformer as an additional economic benefit. The process of the invention can be operated under conditions to maintain an H2/hydrocarbon molar ratio in the range of 0.5:1 to 10:1. An H2/hydrocarbon molar ratio in the range of 1:1 to 4:1 is exemplary.

[0069] In another embodiment, the process of the invention to produce para-xylene can be incorporated into a multistage naphtha reforming process after a separation stage, for example, after a fractional distillation of the effluent from a penultimate stage . For example, effluent from a penultimate stage of a multistage naphtha reforming process can be separated into at least one C8-containing stream by processes such as fractional distillation. The C8-containing flux comprises at least about 5% by weight of C8 paraffinic hydrocarbons or at least about 10% by weight of C8 paraffinic hydrocarbons or at least about 12% by weight of C8 paraffinic hydrocarbons, or even about 15% by weight of C8 paraffinic hydrocarbons. This flow can be contacted with the catalyst used in the process of the invention in a separate stage under para-xylene formation reaction conditions as described above.

[0070] In one embodiment, the process of the present invention can be isolated. By "isolated" it is meant that the process of the invention is carried out in a separate reactor. Exemplary, non-limiting examples of feedstocks comprising at least about 10% by weight of C8 paraffinic hydrocarbons include a naphtha fraction from a hydrocracking reactor, naphtha fractions from direct cycle, naphtha derived from fluid catalytic cracking or combinations thereof .

[0071] In yet another embodiment, the process of the invention can be integrated into a hydrocracking process. The hydrocracker can directly supply paraffinic C8-containing feed material to the process of the invention. Generally, a hydrocracker can utilize a variety of hydrocarbonaceous feedstocks, such as gas oils and heavy gas oils. A typical gas oil comprises a substantial portion of hydrocarbon components boiling above about 560.9 K (550°F), usually at least about 50 percent by weight boiling above 560.9 K ( 550°F). A typical vacuum gas oil typically has a boiling point range between about 588.7 K (600°F) and about 838.7 K (1050°F). Hydrocarbon feedstocks that may be hydrocracked by the hydrocracker include all mineral oils and synthetic oils (eg, shale oil, bituminous sand products, etc.) and their fractions. Illustrative hydrocarbon feedstocks include those comprising boiling point components above 560.9 K (550°F), such as atmospheric gas oils, vacuum gas oils, vacuum and atmospheric asphalt residues, hydrotreated waste oils, coker distillates, direct cycle distillates, pyrolysis-derived oils, high boiling point synthetic oils, various petroleum distillates, cycle oils and catalytic cracker distillates. One skilled in the art will appreciate that the scope of the present process encompasses a number of specific hydrocracker process configurations, including single-stage and two-stage hydrocracking, including one-time feed and recycle operation, and including the presence or absence of one or more more distillation stages, including atmospheric pressure distillation and vacuum distillation.

[0072] Reference is now made to an embodiment of the invention illustrated in Fig. 1. A hydrocarbon feedstock 2 boiling above about 560.9 K (550°F) passes into reaction zone 10 and is contacted with a hydrocracking catalyst. Reaction zone 10 may contain one or more beds of the same or different catalyst. Hydrocracking of hydrocarbon feedstock 2 in contact with a hydrocracking catalyst in reaction zone 10 is conducted in the presence of hydrogen and preferably under hydrocracking conditions that include a temperature of about 505.37 K (450° F) (232°C) to about 755.37 K (900°F) (482°C), a pressure of about 3.44 MPa (500 psig) to about 34.4 MPa (5000 psig), a liquid hourly space velocity (LHSV) of about 0.1 to about 15 h-1, and a hydrogen circulation rate of about 500 to about 5000 standard cubic feet per barrel. Hydrogen is introduced through a fresh hydrogen feed 4 and hydrogen recycle circuit 42.

[0073] The effluent 12 from the hydrocracking reaction zone 10 comprises C8 paraffinic hydrocarbons. In the embodiment illustrated in Fig. 1, the effluent is separated in the separation zone 20 into a hydrogen-containing stream 22, one or more light streams 24 (comprising, for example, C7 hydrocarbons), a C8-containing hydrocarbon stream 26 (comprising at least about 10% by weight of C8 paraffinic hydrocarbons) and one or more heavy streams 28 (comprising, for example, C9+ hydrocarbons) and a waste stream 29. In embodiments, this separation takes place in a single separation zone using a fractionating column. In other embodiments, this separation is done in sequential zones, with the hydrogen and, optionally, the C4- stream separated in one or more preliminary separation zones, prior to separating the C8-containing hydrocarbon stream 26 and the heavy stream 28 Unreacted material can be recycled back to reaction zone 10 or passed to an optional second reaction zone for further cracking. The C8-containing hydrocarbon stream comprising at least about 10% by weight of C8 paraffinic hydrocarbons is passed to a reforming reaction zone 40. The C8 paraffinic hydrocarbons may be further heated before passing to the paraffinic reaction zone 40. xylene. In the process of the invention, the C8 paraffinic feed stream is contacted with a catalyst comprising a silicalite molecular sieve having a silica to alumina mole ratio of at least about 40 to 1. para-xylene include a pressure between 0 MPa (0 psig) to 2.41 MPa (350 psig), a temperature between 259.8 to 866.48 K (800 to 1100°F), and a flow rate between 0.1 h-1 to 20 h-1 of LHSV.

[0074] The product stream 44 from the para-xylene reaction zone 40 comprises C8 aromatic hydrocarbons including para-xylene and meta-xylene in a weight ratio of para-xylene to meta-xylene of at least 0.9. In embodiments, the weight ratio of para-xylene to meta-xylene is at least 1.0 or at least 1.1 or at least 1.2. The para-xylene reaction zone also produces hydrogen 42. This hydrogen can be recycled to the hydrocracker reaction zone 10. The generation of hydrogen by the process of the invention provides an economic benefit by minimizing the additional hydrogen required for the para-xylene reaction zone. hydrocracking. The para-xylene in the product stream 44 can be separated by any suitable method, such as passing it through a water condenser and subsequently passing the organic phase through a column in which the chromatographic separation of the xylene isomers is realized. Another method for separating para-xylene from other isomers and from hydrocarbon compounds is crystallization, in which the para-xylene containing product is cooled to produce predominantly para-xylene crystals, the para-xylene-containing stream 54 is removed by any means. suitable as filtration and/or centrifugation. The remaining hydrocarbons can be recycled as C8 feed material for the process of the invention. The para-xylene thus formed can be separated as described above by means of filtration and/or centrifugation, for example. The depleted para-xylene 52 product stream can then be recycled back to the reforming reaction zone for further processing.

[0075] The process of the invention may be repeated in subsequent reaction rounds until the C8-containing feed material is depleted of C8 paraffinic hydrocarbons, such that the feedstock comprises at least 5% by weight of C8 paraffinic hydrocarbons.

[0076] The following examples are presented to exemplify embodiments of the invention, but are not intended to limit the invention to specific embodiments. Unless otherwise indicated, all parts and percentages are by weight. All numerical values are approximate. When numerical ranges are given, it should be understood that embodiments outside the stated ranges may still fall within the scope of the invention. Specific details described in each example are not to be construed as necessary aspects of the invention.

EXAMPLES Example 1.

[0077] A naphtha feed material comprising more than 10% C8 paraffinic hydrocarbons, with a simulated distillation ASTM D-2887 shown in Table 1, was used as a feed for the process of the invention and the following comparative examples (IBP = initial boiling point, EP = final boiling point). The composition of the feed material was characterized by API, RON and GC analysis, with results shown in Table 2, where B represents benzene, T represents toluene, X for all three xylene isomers and EB for ethylbenzene, while PX/MX represents the yield ratio of para-xylene to meta-xylene.

[0078] Table 1: ASTM D-2887 simulated feed distillation

[0079] Table 2: Other feed properties

Example 2. (Comparative)

[0080] The naphtha feed described in Example 1 was contacted in a fixed bed reactor containing a commercial amorphous reforming catalyst comprising platinum with a rhenium promoter on an alumina support. Reaction conditions included temperatures of 747.03; 752.59; 758.15; 763.7 K (885, 895, 905, and 915°F), a pressure of 350 psig, a liquid hourly space velocity (LHSV) of 1.5 h-1, and a hydrogen to hydrocarbon mole ratio of 5:1 .

[0081] The yield of liquid C5+, its RON and other properties, as well as the hydrogen production obtained under the aforementioned conditions are listed in Table 3, where HC means hydrocarbons and H2/HC the molar ratio of hydrogen to hydrocarbons in the reactor inlet. A PX/MX ratio of about 0.41 was obtained for all products at these four temperatures.

[0082] Table 3: Properties of reforming products obtained from a commercial reforming catalyst comprising platinum with a rhenium promoter on an alumina support.

Example 3. (Invention)

[0083] The naphtha feed described in Example 1 was contacted in a fixed-bed reactor containing a ZSM-5 zeolite-based catalyst compounded with 30% by weight of alumina binder material. The ZSM-5 had a SiO2/Al2O3 molar ratio of about 500 and was ion exchanged to the ammonium form before incorporating 70 wt% zeolite into 30 wt% alumina extrudate. The extrudate was impregnated with 0.8% by weight Pt, 0.38% by weight Re, 0.35% by weight Na and 0.3% by weight Mg by an incipient wetness procedure to make the catalyst Final. Reaction conditions included temperatures of 735.92 (865), 741.48 (875), 747.03 (885), 752.59 (895), 758.15 (905) and 763.7 (915°F ), a pressure of 0.55 MPa (80 psig), a liquid hourly space velocity (LHSV) of 1.0 h-1, and at a hydrogen to hydrocarbon molar ratio of 2:1.

[0084] The yield of liquid C5+, its RON and other properties, as well as the hydrogen production obtained under the above conditions are listed in Table 4. The PX/MX ratio of the products produced over ZSM-5 zeolite-based catalyst in this example ranged from 1.02 to 1.32.

[0085] Table 4: Properties of reforming products obtained from a catalyst based on ZSM-5.

Example 4 (invention)

[0086] The naphtha feed is prepared by a distillation process suitable to produce a naphtha feed having a high amount of C8 hydrocarbons. In this example, the naphtha feed contains more than 40% by weight of C8 hydrocarbons, of which more 40% by weight are C8 paraffins. The para-xylene/meta-xylene weight ratio of the naphtha feed is in the range of 0.4 to 0.45. This naphtha feed is contacted in a fixed-bed reactor containing a ZXM-5 zeolite-based catalyst, as described in Example 3. The para-xylene/meta-xylene molar ratio of the reformed product is greater than 1, 0.

[0087] As demonstrated in the above examples, the process of the invention provides high para-xylene yield compared to a conventional process for making para-xylene. The process of the invention also gave a much higher PX/MX ratio compared to the comparative example process. Comparing the PX/MX ratios in Tables 3 and 4, the paraselectivity of the ZSM-5 zeolite-based catalyst used in the process of the invention is clearly demonstrated.

Claims (15)

1. Process for producing para-xylene, characterized in that it comprises the steps of: (a) supplying a C8-containing feed material which contains at least 10% by weight of paraffinic C8 hydrocarbons to a reforming reaction zone which contains a reforming catalyst comprising a medium pore zeolite having a silica to alumina molar ratio of at least 200 and a crystallite size of less than 10 microns; (b) contacting the C8-containing feed material under reforming reaction conditions in the reforming reaction zone, to produce para-xylene and meta-xylene at a weight ratio of para-xylene to meta-xylene of at least 0, 9; and (c) separating the para-xylene from the meta-xylene; wherein step (a) comprises supplying a C8-containing feed material to a reforming reaction zone containing a reforming catalyst comprising a medium pore zeolite having a silica to alumina mole ratio of at least 200, a crystallite size less than 10 microns, an alkaline content less than 5000 ppm and in the range between 0.1% by weight and 1% by weight of platinum, rhenium, or combinations thereof. wherein step (b) comprises contacting the C8-containing feed material under reforming reaction conditions including a pressure between 0 MPa (0 psig) to 2.41 MPa (350 psig), a temperature between 699.81 K to 866 .48 K (800°F to 1100°F) and a flux rate between 0.1 h-1 to 20 h-1 of LHSV. 2. Process according to claim 1, characterized in that step (a) comprises supplying the C8-containing feed material to the reforming reaction zone containing a reforming catalyst comprising ZSM-5. 3. Process according to claim 1, characterized in that step (a) comprises supplying the C8-containing feed material to the reforming reaction zone containing a reforming catalyst comprising silicalite. 4. Process according to claim 1, characterized in that step (a) comprises supplying the C8-containing feed material to the reforming reaction zone containing a reforming catalyst comprising a medium pore zeolite having a silica to alumina molar ratio of at least 200, a crystallite size of less than 10 microns, and an alkaline content of less than 5000 ppm. 5. Process according to claim 1, characterized in that step (b) further comprises producing para-xylene and meta-xylene in a weight ratio of at least 1.0. 6. Process according to claim 1, characterized in that step (b) further comprises producing para-xylene and meta-xylene in a weight ratio of at least 1.1. 7. Process according to claim 1, characterized in that step (b) further comprises producing para-xylene and meta-xylene in a weight ratio of at least 1.2. 8. Process according to claim 1, characterized in that step (c) comprises separating the para-xylene from the product stream and still recovering a depleted para-xylene product stream. 9. Process according to claim 8, characterized in that it further comprises recycling the exhausted para-xylene product flow to the reforming reaction zone. 10. Process according to claim 8, characterized in that step (c) comprises separating the para-xylene from the product stream by crystallization. 11. Process for producing para-xylene, characterized in that it comprises the steps of: (a) contacting a hydrocarbonaceous feed in which at least 50% by weight of said feed boils above 560.93 K (550°F) in a first reaction zone comprising a hydrocracking catalyst under hydrocracking conditions to form an effluent; (b) separating the effluent into at least one C8-containing fraction comprising at least 10% by weight of C8 paraffinic hydrocarbons; (c) feeding the C8-containing fraction to a second reaction zone; (d) contacting the C8-containing fraction under reforming reaction conditions with a reforming catalyst comprising a medium pore zeolite having a silica to alumina molar ratio of at least 200, a crystallite size of less than 10 microns and a content of alkali less than 5000 ppm in a second reaction zone, to produce a product stream comprising para-xylene and meta-xylene, wherein the ratio of para-xylene to meta-xylene is at least 0.9; and (e) separating the para-xylene from the product stream. wherein step (a) comprises supplying a C8-containing feed material to a reforming reaction zone containing a reforming catalyst comprising a medium pore zeolite having a silica to alumina molar ratio of at least 200, a crystallite size less than 10 microns, an alkaline content less than 5000 ppm and in the range between 0.1% by weight and 1% by weight of platinum, rhenium, or combinations thereof, where step (b) comprises contacting the Feed material containing C8 under reforming reaction conditions including a pressure between 0 MPa (0 psig) to 2.41 MPa (350 psig), a temperature between 699.81 K to 866.48 K (800°F to 1100° F) and a flow rate of between 0.1 h-1 to 20 h-1 of LHSV, where the hydrocracking conditions comprise a temperature between 505.37 K to 755.37 K (450 to 900°F), a pressure between 3.44 to 34.4 MPa (500 to 5000 psig), an LHSV between 0.1 to 3015, and a hydrogen circulation rate between 2000 to 5000 standard cubic feet per barrel; where the reforming reaction conditions include a pressure between 0 MPa to 2.41 MPa (0 psig to 350 psig), a temperature between 699.81 K to 866.48 K (800°F to 1100°F), and a flow rate between 0.1 h-1 to 20 h-1 of LHSV. 12. Process according to claim 11, characterized in that it additionally comprises the step of recovering an exhausted para-xylene product stream. 13. Process according to claim 12, characterized in that it additionally comprises the step of recycling the exhausted para-xylene product stream to the second reaction zone. 14. Process according to claim 11, characterized in that it further comprises generating hydrogen from the second reaction zone. 15. Process according to claim 14, characterized in that the hydrogen is recycled to the first reaction zone.

Images